The present invention relates to securing an arc runner to a load or line strap, and more particularly, to securing an arc runner to a load or line strap without using hardware or a mechanical operation.
Circuit breakers are one of a variety of overcurrent protective devices used for circuit protection and isolation. The basic function of a circuit breaker is to provide electrical system protection whenever an electrical abnormality occurs in any part of the system. In a circuit breaker, current enters the system from a power line. The current passes through a strap to a stationary contact fixed on the strap and then to a movable contact. The movable contact is fixedly attached to an arm, and the arm is mounted to a rotor. As long as the stationary and movable contacts are in physical contact, current passes from the stationary contact to the movable contact and out of the circuit breaker to down line electrical devices.
In the event of an overcurrent condition (e.g., a short circuit), extremely high electromagnetic forces are generated. These electromagnetic forces repel the movable contact away from the stationary contact. Because the movable contact is fixedly attached to a rotating arm, the arm pivots and physically separates the stationary and movable contacts thus blowing open (tripping) the circuit. Upon separation of the contacts and blowing,open the circuit, an arcing condition occurs. It is desirable to suppress the resultant arc in order to avoid a hazardous condition. The typical method of suppressing the arc is to direct it into an arc chute, which is generally a series of metal plates that dissipate the energy of the arc. This arc chute is situated proximate to the stationary contact point of the circuit.
An arc runner is used to direct the arc to the arc chute. The arc runner substantially covers the exposed area of the stationary contact disposed on the strap. Blowing a circuit open thus resulting in an arc causes tremendous stress to the parts of the system. Since the arc runner provides a pathway for the arc to follow to the arc chute, it is subject to intensely high temperatures. The construction of an arc runner, and especially its manner of seducement to the strap, is critical to reliable dissipation of an arc.
Conventional methods of securing an arc runner to a load or line strap increase the costs of manufacturing a circuit breaker because of the hardware involved. The arc runner is typically screwed onto the strap, as described in U.S. Pat. No. 5,877,467 entitled "Circuit Breaker Current Limiting Arc Runner". Similarly, U.S. Pat. No. 5,075,520 entitled "Contact Member for Electrical Switching Devices" describes an arc runner having one end inserted into a groove in a block and then having the arc runner secured to the block by a screw. The use of a screw in the fastening operation adds the cost of an extra piece of hardware to the manufacturing process.
Bolts are also used to secure an arc runner to a strap. For example, U.S. Pat. No. 4,229,630 entitled "Circuit Breaker Utilizing Improved Arc Chambers" describes using a pair of bolts that extend through openings in an arc runner to secure the arc runner to a stationary contact. Another method of securing an arc runner to a strap includes the use of rivets, as discussed in U.S. Pat. No. 4,771,140 entitled "Circuit Interrupter", wherein a single rivet pierces the body of an arc runner and a stationary conductor to firmly connect the arc runner to the stationary conductor. Bolts and rivets add the cost of an extra piece of hardware to the manufacturing process in the same way that screws do.
Welding, as discussed in U.S. Pat. No. 5,818,003 entitled "Electric Switch with Arc Chute, Radially Converging Arc Splitter Plates, and Movable and Stationary Arc Runners", provides a further option for securing an arc runner to a strap, wherein the strap is directly welded to a D-shaped arc runner. Although welding does not introduce an additional discrete component into the manufacturing process, it does contribute to the expenses associated with the finished product.
In addition to the costs of the hardware used to fasten the arc runner to the strap, tools are required. Automated assembly systems and automated welders are usually expensive to install and run. Furthermore, the maintenance for these systems is costly, and the use of such systems often poses reliability concerns. Hand-held tools such as wrenches and screwdrivers, on the other hand, are far less expensive. The use of small hand-held tools may, however, increase the time required for assembly of an arc runner to a load strap because machine assembly is usually faster than hand assembly is. An increase in the time required for assembly using hand-held tools is becoming cost prohibitive. Furthermore, hand-held tools, because of their size, frequently tend to be misplaced and need to be replaced on a regular basis. Constant replacement of even the most inexpensive tools can be a limiting factor.